Since 2000, Democrats gained class 1 US Senate seats during the 2000,2006,2012,and 2018 cycle.
2000
Democrats picked up DE,FL,MI,MN,MO,and WA but lost NV and VA. +4D
2006
Democrats picked up MO,MT,OH,PA,RI,and VA. +6D
2012
Democrats picked up IN,ME,and MA but lost NE. +2D
2018
Democrats will pick up AZ,NV,TN,and TX and hold onto every Democratic held seat up in 2018. +4D
Here is what the 2024 US Senate Election will look like.
OPEN seats
CA (Feinstein-D) Democratic hold.
DE (Carper-D) Democratic hold.
FL (Nelson-D) Democratic hold if Gillum-D runs. Tossup otherwise.
ME(King-I/D) Democratic hold.
MD(Cardin-D) Democratic hold.
TN(Bredesen-D) Democratic loss.
VT(Sanders-I/D) Democratic hold.
Vulnerable Democratic incumbents
AZ-(Sinema-D) Democratic hold.
IN-(Donnelly-D) Tossup with Holcomb-R
MO(McCaskill-D) Tossup with Parson-R
MT(Tester-D) Democratic hold
NV(Rosen-D) Democratic hold
ND(Heitkamp-D) Tossup with Burgum-R or Armstrong-R
TX(O'Rourke-D) Tossup with Bush-R
WV(Manchin-D) Democratic hold.
Democrats will lose seats during the 2024 US Senate Election cycle but if 2024 is a favorable year for Democrats( Democrats favored to win the White House), Democrats will hold onto every Democratic held seat up in 2024 except TN.